The objective of this application is to develop advanced optrode solutions for neuroscientists that fulfill the potential of optogenetic technology-achieving highly specific neural circuit control. Once developed, the neuroscientist's experimental options for optical stimulation will grow to two dimensions with no limits on the recording site placement. Our approach develops (i) practical, yet novel solutions for the packaging issues currently plaguing users, and (ii) custom waveguides capable of region-specific illumination with no electrical artifact, and is modularly integrated onto any existing NeuroNexus recording array. As an alternative to wafer- level integration, we have devised an approach that lowers cost by improving yield while increasing design options. This project will further optogenic techniques, which have shown excellent promise as tools that allow temporally precise, non-invasive control of activity in well- defined neuronal populations. This degree of control over neural firing allows specific monitoring of temporal activity patterns in the context of circuit dynamics, understanding changes due to plasticity, and responses to behavior and external cues, which is critically important for studying disease models as well. PUBLIC HEALTH RELEVANCE: The objective of this application is to develop advanced optrode solutions for neuroscientists that fulfill the potential of optogenetic technology-achieving highly specific neural circuit control. Once developed, the neuroscientist's experimental options for optical stimulation will grow to two dimensions with no limits on the recording site placement. Our approach develops (i) practical, yet novel solutions for the packaging issues currently plaguing users, and (ii) custom waveguides capable of region-specific illumination with no electrical artifact, and is modularly integrated onto any existing NeuroNexus recording array. As an alternative to wafer- level integration, we have devised an approach that lowers cost by improving yield while increasing design options. This project will further optogenic techniques, which have shown excellent promise as tools that allow temporally precise, non-invasive control of activity in well- defined neuronal populations. This degree of control over neural firing allows specific monitoring of temporal activity patterns in the context of circuit dynamics, understanding changes due to plasticity, and responses to behavior and external cues, which is critically important for studying disease models as well.